Juice is defined as a drink containing 100% of that which may be extracted from fruit, vegetables or berries and which normally contains no additives. Beverages with a lower content are normally designated nectar or fruit drinks. For the production of juices, a common process is to take, as the point of departure, a juice concentrate extracted from the fruit or fruits which the intention is to use.
In a class on its own as the commonest juice beverage on the market is orange juice. However, the oranges are most generally not cultivated in those countries which are the major consumers of juice. In order to economise on transport costs of orange juice from the grower countries to the consumer countries, it is therefore necessary to concentrate the juice in the country of origin and transport the concentrate, which then constitutes only 15-20% of the finished juice product. Most generally, the concentrate is transported in the frozen state. In the consumer country, the concentrate must thereafter be diluted with water, i.e. it must be reconstituted in order to reassume its pristine composition and concentration. More than 90% of the world's orange juice production takes place in this manner.
The commonest method for reconstituting is that concentrate and water are mixed, either batchwise in large tanks or continuously in specific process equipment. Thereafter, the finished juice is pasteurised, cooled and packed in consumer packages. Methods which directly supply superheated water to the concentrate also exist. In this case, the product is thereafter cooled indirectly and packed in consumer packages.
Also in the production of juice from concentrate, so-called reconstituted juice, the aim is to approximate the flavour of freshly pressed juice, which is normally consumed immediately after extraction. Above all two factors affect the quality of the juice during this process, temperature and oxygen. In order to improve the product, attempts are made to expose the juice to as slight thermal action as possible, at the same time as it is important to obtain a product with reasonable shelf-life. The process should also be designed so that the action of oxygen is minimised. Oxygen oxidises and destroys vitamin C and thereby reduces the nutrient content of the juice.
At the same time, the process must be made rational with as short start- and stop-times as possible. The process should also be flexible so that it is possible to switch product rapidly and simply without major product losses. The process should also be capable of being used for different types of fruit or vegetable juices, including those which contain fibres.
One such method is described in U.S. Pat. No. 4,684,531. Steam is supplied to the juice concentrate so that a pasteurisation temperature is attained. The partly diluted juice concentrate is kept at this temperature during a given interval of time. Thereafter, water is added in the quantity required to obtain a reconstituted juice. The finished juice is thereafter packed in aseptic consumer packages.
In a plant for the production of juice, as described above, it may naturally occur that brief production stoppages happen because the filling machine temporarily stops. During these brief stoppages, which may be up to 15 minutes, it is vital to maintain aseptic conditions in the plant.
In other juice plants where hot water is added to the concentrated juice, it is only the supply of concentrate and water which has been stopped, and the quantity of juice which is in the buffer tank has had time to cool below pasteurisation temperature. In order to avoid a temperature alarm immediately after restart, the temperature signal has, in this instance, been masked. However, this procedure entails that there is a risk that a minor quantity of product in or ahead of the mixing tank is not sufficiently pasteurised.
In conventional pasteurisation plants for juice, using heat exchangers, the product is recycled over the pasteuriser constantly during brief stoppages. This entails that there is considerable consumption of energy even during operational stoppage.